The invention relates to a burner-lance unit comprising at least two gas connections, a burner tube, and a lance tube which is arranged within the burner tube and is concentric thereto, wherein each of the burner tube and the lance tube has a gas inlet end and a gas outlet end, and wherein the gas outlet end of the lance tube has a de Laval nozzle which is releasably connected to the lance tube. The invention furthermore relates to a furnace having at least one such burner-lance unit.
Such a burner-lance unit is known from DE 196 37 246 A1. It is formed by a combination of a burner and a lance, wherein operation of such a unit can be carried out either in burner mode or in lance mode.
Metallurgical furnaces, especially arc furnaces, preferably have burners which are installed on the furnace wall and are directed onto the surface of the molten metal in the furnace chamber in order to introduce energy into the molten metal or in order to accelerate the melting process in the furnace. A flame is formed in burner mode by such a burner. In the process, fuel, especially natural gas, oil and the like, is combusted with the addition of a combustible gas containing oxygen.
Lances are customarily introduced into the furnace chamber locally and frequently at limited times in order to feed for example gases, such as oxygen for oxidizing the molten metal, to carry out measurements, or to take samples.
As in a conventional burner, a flame is also created in a burner-lance unit when it is operated in burner mode and energy is introduced into the furnace chamber. After shutting off the burner mode, i.e. shutting off the flame, the burner-lance unit can be used as a lance via which a gas flow can be blown into the furnace chamber and, if necessary, measurements can be carried out on the molten metal. To this end, gas connections for at least one gas which is to be blown in in lance mode are provided on a burner-lance unit in addition to the connections for fuel and combustible gas which are provided on a conventional burner. By the use and modification of a conventional burner to form a burner-lance unit in such a way that this can also be used as a lance, no additional cost and no space requirement for additional devices therefore arises.
In the lance mode, the interior of the burner-lance unit can be used in order to carry out a temperature measurement on the molten metal in the furnace chamber by means of a temperature measuring unit. In this case, gas to be blown in at supersonic speed in lance mode is especially injected into the furnace chamber in the direction of the molten metal in order to blow away slag which forms on the molten metal and to locally expose the surface of the molten metal for a contactless temperature measurement. In order to create a gas flow which is to be blown in at supersonic speed, the burner-lance unit especially has a de Laval nozzle into which the gas is fed, at several bar pressure.
A burner-lance unit with a temperature measuring device is described in WO 2011/018 403 A1.
A burner-lance unit, which comprises at least two gas connections, a burner tube and a lance tube which is arranged within this burner tube concentrically thereto, is known from U.S. Pat. No. 5,599,375 A. The burner tube and the lance tube have in each case a gas inlet end and a gas outlet end. The lance tube at its gas outlet end has a de Laval nozzle. A head element, which forms a combustion space and is water cooled, is flanged onto the burner tube. The head element has discharge openings through which the combustible gas which is directed in the burner tube can flow into the combustion space.
The standard operation of a metallurgical furnace having at least one burner-lance unit is customarily carried out in this case as follows:
During the feeding of the material to be melted into the furnace chamber the burner-lance unit is operated with a protected flame in order to keep the opening of the burner-lance unit which is directed towards the furnace chamber clear. The burner-lance unit is then operated in burner mode and the output is increased in steps in order to support melting of the material in the furnace chamber. As soon as there is a sufficient quantity of molten metal, the burner-lance unit is switched into the lance mode and oxygen, or gas containing oxygen, is injected into the furnace chamber at supersonic speed for oxidizing the molten metal. During lance mode, the protected flame is customarily burnt again, enveloping the injected gas flow. As soon as the furnace can be tapped off, i.e. as soon as the furnace chamber can be emptied, the gas flow is shut off, the burner-lance unit is further operated with the forming of the protected flame, and the molten metal is withdrawn. The standard operation now begins from new with the feeding of material, which is to be melted, into the furnace chamber.
The side of the burner-lance unit which projects into the chamber of the furnace, the so-called “hot” end, is in this case subjected to sharp temperature changes and also to high mechanical and corrosive loads. Especially the end region, at which the gas outlet openings of the burner tube and of the lance tube are located, becomes very hot and therefore particularly severely stressed. The service life of a burner-lance unit therefore mainly depends on the state of this end region.
On account of the specific type of construction of the de Laval nozzle, this nozzle is produced as a separate part and is then releasably connected to the lance tube so that in the event of excessive wear, this nozzle can be exchanged. In the event of wear in the region of the gas outlet end of the burner tube, this tube is exchanged completely for a new burner tube, wherein the burner-lance unit has to be totally dismantled in a time-intensive maintenance process and then reassembled again.
A burner-lance unit, which has two gas connections and a lance tube, is known from WO 2012/089 754 A2, wherein the lance tube has a gas inlet end and a gas outlet end. The lance tube at its gas outlet end has a de Laval nozzle. The lance tube is encompassed by a cooling tube.
A plurality of embodiments are known from WO 96/06954 A1.
In one embodiment, WO 96/06954 A1 shows a burner-lance unit which has at least two gas connections, a burner tube and a lance tube which is concentrically arranged within the burner tube, wherein each of the burner tube and the lance tube has a gas inlet end and a gas outlet end, wherein the lance tube has a de Laval nozzle at its gas outlet end, and furthermore the burner tube has a burner nozzle which is releasably connected to the burner tube.
In another embodiment, WO 96/06954 A1 shows a burner-lance unit which comprises at least two gas connections, a burner tube and a lance tube which is arranged within this burner tube concentrically thereto. Each of the burner tube and the lance tube has a gas inlet end and a gas outlet end. The burner tube is arranged concentrically inside a cooling tube.
In yet another embodiment, WO 96/06954 A1 shows a burner-lance unit in which an inner, central tube is concentrically encompassed by two further tubes. The innermost tube carries water, and the two outer tubes carry an oxygen-rich gas and a liquid combustible material. Positioned upstream of the tubes is a combustion chamber which is described as being water cooled.
In yet another embodiment, WO 96/06954 A1 shows a burner-lance unit which comprises at least two gas connections, a burner tube and a lance tube which is arranged within this burner tube concentrically thereto. Each of the burner tube and the lance tube has a gas inlet end and a gas outlet end. The burner tube is arranged inside a cooling tube. The burner tube has a burner nozzle which is encompassed by the cooling tube.
A burner-lance unit comprising at least two gas connections, a burner tube and a lance tube which is arranged concentrically to the burner tube, is known from WO 02/44617 A1. Each of the burner tube and the lance tube has a gas inlet end and a gas outlet end.
A burner-lance unit comprising at least two gas connections, a burner tube and a lance tube which is concentrically arranged within the burner tube, is known from WO 99/54511 A1. Each of the burner tube and the lance tube has a gas inlet end and a gas outlet end. The lance tube at its gas outlet end has a de Laval nozzle.